Classification of binding property of amyloid to lipid membranes: Membranomic research using quartz crystal microbalance combined with the immobilization of lipid planar membranes

A biomembrane-related fibrillogenesis of Amyloid beta from Alzheimer' disease (A beta) is closely related to its accumulation behavior. A binding property of A beta peptides from Alzheimer' disease to lipid membranes was then classified by a quartz crystal microbalance (QCM) method combined with an immobilization technique using thiol self-assembled membrane. The accumulated amounts of A beta, Delta f(max), was determined from the measurement of the maximal frequency reduction using QCM. The plots of Delta f(max) to A beta concentration gave the slope and saturated value of Delta f(max), (Delta f(max))(sat) that are the parameters for binding property of A beta to lipid membranes. Therefore, the A beta-binding property on lipid membranes was classified by the slope and (Delta f(max))(sat). The plural lipid system was described as X + Y where X = L-1, L-1/L-2, and L-1/L-2/L-3. The slope and (Delta f(max))(sat) values plotted as a function of mixing ratio of Y to X was classified on a basis of the lever principle (LP). The LP violation observed in both parameters resulted from the formation of the crevice or pothole, as A beta-specific binding site, generated at the boundary between l(d) and l(o) phases. The LP violation observed only in the slope resulted from glycolipid-rich domain acting as A beta-specific binding site. Furthermore, lipid planar membranes indicating strong LP violation favored strong fibrillogenesis. Especially, lipid planar membranes indicating the LP violation only in the slope induced lateral aggregated and spherulitic fibrillar aggregates. Thus, the classification of A beta binding property on lipid membranes appeared to be related to the fibrillogenesis with a certain morphology.